1. Field of the Invention
The subject invention is directed to the field of sensing, autonomous measurement, and wireless communications, and more particularly to, the use of wireless sensors in rotorcraft Rotor Track and Balance (RTB) systems.
2. Background of the Related Art
Wireless sensing has been steadily gaining ground in the aerospace industry. In some applications, data is collected via a set of sensors which are remotely located from data processors. The sensors are connected to these data processors through a heavy harness of numerous and long wires. However in certain applications, these sensors or actuators need to be situated at critical locations, such as near the aircraft engine or on rotating parts of the aircraft making it challenging, if at all possible, to rely on traditional wires and harnesses to provide power to the sensors and a communication link between the sensors and the data processor(s).
Establishing a wireless link instead of using physical wires to communicate with sensors can lead to substantial weight and cost savings in many aerospace applications, but replacing wires with wireless communications is not a simple process. Particular challenges exist when using wireless methods that do not exist in wired systems, such as discontinuous data acquisition, data synchronization, sensor power supply and conservation and others.
In rotorcraft, excess vibration levels lead to premature wear and in some cases to catastrophic failures in rotating components. To improve the safety and readiness of rotorcraft planes it is thus essential to minimize vibration levels in the airframe. Health and Usage Monitoring Systems (HUMS) use vibration measurements to diagnose mechanical health of the aircraft and to suggest possible corrective actions.
Rotor Track and Balance, a function performed by the aircraft HUMS, is the process of detecting and correcting vibrations caused by the main rotor. Vibrations caused by the helicopter main rotor are typically either in a vertical or lateral plan (with respect to the main frame of the rotorcraft) that are respectively due to unequal lift produced by the main rotor blades or to unequal distribution of mass in the main rotor “disk.” There are several reasons that can cause these types of undesired vibrations. For instance, most common causes of vertical vibration include variation between chord profiles of the blades and inadequate adjustment of pitch change links and trim tabs.
For the lateral vibration case, minor discrepancies in the manufacturing process may cause blade and other weight differences which may lead to unequal distribution of mass in the main rotor. Moreover, aging and many other reasons can be behind vertical and lateral vibrations in the main rotor. As such, tracking the main rotor vibration profile and taking corrective action to smooth such vibration is the objective of the Rotor Track and Balance system.
The most common corrective action is to place weights on the main rotor hub at specific locations. There are two types of data that need to be acquired to perform RTB: track data and vibration data. Track data is typically acquired using an optical tracker sensor, while vibration data is acquired using accelerometers. For correct interpretation of vibration data, rotor azimuth position sensors, sometimes referred to as tachometer sensors, are also included in RTB systems. Note that the rotor track adjustment feature may be optional and the optical tracker sensor may not be always deployed. Then, vibration and azimuth data alone may be used for rotor balancing only. Traditionally, such limited installations have been also referred to as RTB systems, as they can be always temporarily expanded by addition of rotor track measurement. The present invention pertains primarily to the rotor balancing function of an RTB system, but is also applicable to full installations that also include the rotor track adjustment function. Exemplary rotor track and balance systems are illustrated in U.S. Pat. Nos. 4,531,408; 4,112,774; 4,053,123; and 6,453,669, each of which are herein incorporated by reference in their entirety to the extent they do not conflict with the present disclosure.
In certain rotorcraft constructions, each of the sensors used to collect data in a Rotor Track and Balance system is placed in close proximity to the main rotor and remotely from the helicopter's HUMS. Therefore, it would be advantageous to provide a wireless RTB system that overcomes the disadvantages associated with traditional wired systems (e.g., weight and cable management) and solves the challenges associated with traditional wireless systems, such as discontinuous data acquisition, data synchronization, and sensor power conservation.